DE69917056T2 - METHOD FOR USE IN A DUAL-MODE SATELLITE COMMUNICATION NETWORK - Google Patents

Description

Territory of invention

The invention relates to satellite communication systems and in particular to a satellite and a subscriber unit, which is the ability have both multiple access in code division multiple access and multiple access to be used in time multiplex.

background the invention

TDMA- (TDMA- "time division multiple access" = multiple access time division multiplex) techniques offer a large number of communication channels for telephony services and are ideal for uneven environments. The load in each satellite beam can be due to high subscriber densities in metropolitan areas be uneven. TDMA access schemes allow frequency assignments of beams can be redistributed to hot spots with little use. TDMA systems are therefore optimal for coverage in the western United States, where the cities are more distant from each other than the cities in the east United States.

CDMA (CDMA "code division multiple access") in code division multiplex) techniques are used to provide services which require more uniform services without peak loads to take advantage from the CDMA reuse factor as well as variable data rate services. CDMA is optimal for environments with uniform density and is optimal for covering the eastern United States and Europe, where metropolitan areas overlap.

There is a significant need for a multi-mode system and a subscriber unit that are capable of both TDMA as well as CDMA techniques based on current usage or the load on the system.

WO 98/44656 discloses a radio communication system, where communication between subscriber unit and satellite through use of FDMA / TDMA, CDMA or TD-CDMA techniques is possible.

Short description of the drawings

1 shows a satellite communication system;

2 shows a block diagram of a transmitter system of a satellite;

3 shows a block diagram of a receiver system of a satellite;

4 , shows a block diagram of a transmitter system of a subscriber unit;

5 shows a block diagram of a receiver system of a subscriber unit;

6 FIG. 4 shows a flow diagram of a channel acquisition and management method in accordance with a preferred embodiment of the present invention; FIG.

7 shows a flow diagram of a channel management method according to a preferred embodiment of the invention.

Description of a preferred embodiment

This invention relates to use several access technologies in a communication network. At a preferred embodiment uses the communication network TDMA and CDMA. By using Several access techniques will improve the quality of service and two different ones Types of high-capacity areas can are operated, namely uniform and uneven. A preferred embodiment the invention uses multi-mode subscriber equipment as well a multi-mode satellite communication system to access TDMA and CDMA seamless to use.

A "satellite" as used in this description denotes a man-made object or vehicle that the Earth in non-geostationary Heights (e.g. B. low altitudes or mean heights) or geostationary Circled highs. A "constellation" means a number of satellites that are arranged in orbits to a specific Coverage (e.g. radio communication; remote acquisition, etc.) of a part, of parts or all of the earth. A constellation typically contains multiple rings (or planes) of satellites and can be the same Number of satellites included in each level, although not is required.

1 shows a satellite communication system. Although 1 a very simplified diagram of a communication system 10 illustrated includes the system 10 a number of satellites 20 , any number of subscriber units 30 and any number of base stations 40 , Although the present invention relates to space-based communication systems 10 with at least one satellite 20 applicable in low or medium earth orbit is the satellite 20 preferably part of a number of satelites lites in low orbit around the earth. In alternative embodiments, the satellite 20 be a medium earth orbit satellite or a geosynchronous satellite. The satellite 20 can be in the same satellite network or in different satellite networks, including e.g. B. the Iridium system or the Globalstar network.

The satellite 20 can be one of many satellites in at least one constellation of satellites orbiting the earth. The present invention is also applicable to space-based communication systems 10 with satellites 20 which orbit the earth at any angle of inclination, including polar, equatorial, inclined or other orbital patterns. The present invention is applicable to systems 10 where full coverage of the earth is not achieved (ie where there are "holes" in the communication coverage provided by the constellation) and on systems 10 where there is multiple coverage of areas of the earth (ie more than one satellite is within sight of the particular point on the earth's surface).

In a preferred embodiment of the present invention, each satellite communicates 20 with other neighboring satellites 20 via cross connections. These cross connections form a backbone of the space-based satellite communication system 10 , A call or communication from a subscriber unit positioned at any point on or near the surface of the earth can therefore be routed via a satellite or a constellation of satellites to substantially any other point on the earth's surface. Communication can be from another satellite 20 to a subscriber unit (receiving the call) on or near the surface of the earth. In alternative embodiments, when there are no cross-links, a satellite can 20 with another satellite 20 by routing the call through a base station 40 communicate.

The subscriber units 30 of 1 can be positioned anywhere on the surface of the earth or in the atmosphere above the earth. The communication system 10 can address any number of subscriber units 30 to adjust. The subscriber units 30 are preferably communication devices that are able to send and receive data. The data can be of any type, including, for example, alphanumeric or numeric. For example, the subscriber units 30 a satellite phone or a satellite pager. The subscriber units must continue 30 not be mobile or mobile, but can be fixed in one position for an extended period of time.

A base station 40 communicates with and controls satellites 20 , With the Iridium system, the base station 40 a gateway or a satellite control system. In a preferred embodiment, there may be multiple base stations 40 that are arranged in different regions on earth. For example, a base station 40 in Honolulu, another in Los Angeles and another in Washington DC. Another example is to have separate base stations positioned in every country in the world. The base stations 40 can send satellite control commands to the satellites 20 deliver so the satellites 20 maintain their correct orbital position and perform other essential household tasks. The base stations 40 may also be responsible for receiving call packet data, paging data, or other types of information from the satellite 20 ,

The base stations 40 provide certain basic services in the communication system 10 ready. They provide system access control for subscribers for whom a base station is "at home", for example where information about the subscriber is stored, including information to authenticate subscriber identity and what services are available to that subscriber. The base stations 40 provide system subscribers with access to the public telephone network (PSTN) and they also offer PSTN customers access to system subscribers via the satellite network.

2 shows a block diagram of a transmitter system of a satellite which can be used in relation to the method of the invention. Although the block diagram will be described with reference to a satellite, the block diagram is also applicable to a transmitter of a base station. The satellite's transmitter 20 includes TDMA channelizers / modulators 102 , CDMA channelizers / modulators 103 , D / A (digital-to-analog) converter 106 and 107 , Step-up mixer 110 and 111 and power amplifier 114 and 115 , These parts are well known to those skilled in the art and are commercially available.

There are different paths through the satellite transmitter; one path for a TDMA signal and another path for a CDMA signal. TDMA subscriber channel bits are sent to the TDMA channelizers / modulators 102 are supplied while CDMA subscriber channel bits are supplied to the CDMA channelizers / modulators 103. The channel bits come from packets which are received from the cross connections (from other satellites), supplier connections (from ground stations) or other subscriber connections. These bits are therefore generated from packets that are routed to the subscriber downlink modem.

A channel bit is the basic unit of information that is sent or received. For example, when a user speaks into a subscriber unit (e.g., a satellite phone), the user's voice is sampled and bits of information are generated. The channel bits are encoded, modulated, channeled and finally converted into an RF (radio frequency) signal for transmission over a wireless connection and finally over a satellite or base station to another subscriber unit. A vo coder in the subscriber unit 30 provides an interface between the user and the channel bits in the case of telephony applications. In the case of data, the uncoded channel bits are equivalent to the data bits.

After the channel bits from the channelizers / modulators 102 or 103 received, they are digitally encoded (e.g. error detection and correction), modulated (e.g. TDMA or CDMA) and channeled (e.g. frequency selection, filter function) until they become a D / A converter 106 or 107 to reach. The modulators are used to modulate the channel bits using quadrature phase shift keying (QPSK) or any other access scheme well known to those skilled in the art.

The channelizers 102 . 103 are used to provide special frequency / time slot (TDMA / FDMA) or frequency / code (CDMA / FDMA) channels. For example, TDMA channelizers 102 able to span a spectrum of 10 MHz 240 to "channel" separate frequency channels, each about 41 kHz wide and using 4 time slots. CDMA channelizer 103 can deliver as many as 64 codes (Walsh codes) using perhaps 3 or 4 different frequency bands. Another possibility for CDMA are TD / CDMA channelizers, which can provide 4 time slots with 64 codes in a single frequency band. A TD / CDMA / TDMA channelizer would provide 4 time slots with 64 codes with 3 or 4 different frequency bands. Although the above numbers are preferred, the number of channels or codes made possible by the latest TDMA or CDMA technology can be larger or smaller.

The step-up mixer 110 is with the D / A converter 106 and the power amplifiers 114 connected. The D / A converter 106 and 107 convert that from the TDMA or CDMA channelizers / modulators 102 or 103 received digital signal into an analog signal. The step-up mixer 110 . 111 convert an IF (intermediate frequency) signal into an analog RF signal using a TDMA local oscillator (LO) signal or a CDMA local oscillator signal, e.g. B. RF = LO + IF. The LO signal is generated by an oscillator (hence the term local oscillator LO), which is separate from the transmitter's RF subsystem. The LO- is a CW ("continuous wave" = continuous wave) signal. There are several possible implementations for this LO source, including voltage controlled oscillators (VCOs), synthesizers, etc., which are well known to those skilled in the art. After the RF signals from the power amplifiers 114 . 115 are amplified, they are supported by an antenna (in 2 not shown) sent to subscriber units and / or base stations.

3 shows a block diagram of a receiver system of a satellite. Although the block diagram will be described with reference to a satellite, the block diagram is also applicable to a receiver of a base station. The receiver of the satellite 20 includes an RF (radio frequency) front end 120 , Down mixer 124 and 125 , A / D (analog-to-digital) converter 128 and 129 , TDMA channelizers / demodulators 132 and CDMA channelizers / demodulators 133 , These parts are well known to those skilled in the art and are commercially available.

As in 3 shown is the RF front end 120 with the down mixers 124 and 125 coupled and is able to receive RF signals from subscriber units and base stations. The RF front end 120 comprises an external receiving antenna and a low noise amplifier (LNA = "low noise amplifier"). In an alternative embodiment, and specifically for digital beamforming, the RF front end includes 120 an LNA, a mixer and an A / D converter in one integrated unit.

The RF front end 120 routes the received RF signal to both the TDMA down mixer 124 as well as the CDMA down mixer 125 , The down mixer 124 . 126 pick up the RF signal and convert it from a TDMA-LO signal or a CDMA-LO signal to an IF signal using appropriate signals. The equation IF = RF - LO specifies how the RF signal is converted into an IF signal. The IF signal is then from the A / D converters 128 or 129 converted into a digital signal and into the TDMA channelizers / demodulators 132 or CDMA channelizers / demodulators 133 entered. The channelizers / demodulators 132 . 133 demodulate the digital IF signal, and the demodulated signal bits are converted into a data packet and routed to the appropriate destination, which can be another subscriber connection, a cross connection or a supply connection. The data packets are routed and then the downlink process described above takes place, which varies depending on which connection type is used (subscriber, cross or supplier connection).

4 shows a block diagram of a transmitter system of a subscriber unit which can be used with regard to the method of the invention. The transmitter system includes a TDMA channelizer / modulator 200 , a CDMA channelizer / modulator 202 , a D / A converter 204 , an upward mixer 206 and power amplifier 208 , The in the transmitter system of the subscriber unit 30 Parts used are well known to those skilled in the art and are commercially available. The operation and functions of these parts are similar to those in 2 parts shown and described.

There is a separate path through the transmitter of the subscriber unit for sending TDMA signals and CDMA signals. TDMA subscriber channel bits become the TDMA channelizers / modulators 200 fed while CDMA subscriber channel bits to the CDMA channelizers / modulators 202 to be delivered. The channel bits are encoded, modulated, channeled and finally into an RF ("radio frequency" = radio frequency) Converted signal for sending to a satellite. A vocoder in the subscriber unit 30 provides an interface between the user and the channel bits in the case of a telephony application. In the case of data, the uncoded channel bits are equivalent to the data bits.

If the channel bits from the channelizers / modulators 200 or 202 received, they are digitally encoded (e.g. error detection and correction), modulated (e.g. TDMA or CDMA) and channeled (e.g. frequency selection, filter function) until the output passes the D / A converter 204 reached. The modulators are used to modulate the channel bits using QSPK ("quadrature phase shift keying") or any other access scheme well known to those skilled in the art.

The channelizers 200 . 202 are used to provide special frequency / time slot channels (TDMA / FDMA) or frequency / code channels (CDMA / FDMA). The step-up mixer 206 is with the D / A converter 204 and the power amplifiers 208 coupled. The D / A converter 204 converts this from either the TDMA or CDMA channelizers / modulators 200 . 202 received digital signal into an analog signal. The step-up mixer 206 converts an IF (intermediate frequency) signal into an analog RF signal using either a TDMA local oscillator (LO) signal or a CDMA local oscillator (LO) signal, e.g. B. RF = LO + IF. After the RF signal from the power amplifiers 208 amplified, it is sent from one antenna to a satellite (there may be multiple antennas if the TDMA and CDMA spectrum are separated by an amount greater than the bandwidth of a single antenna).

5 shows a block diagram of a receiver system of a subscriber unit which can be used with regard to the method of the invention. The receiving system of the subscriber unit 30 includes an RF front end 210 , a down mixer 212 , an A / D converter 214 , a TDMA channelizer / demodulator 216 and a CDMA channelizer / demodulator 218 , The in the receiving system of the subscriber unit 30 Parts used are well known to those skilled in the art and are commercially available. The operation and functions of the parts in the receiver system of the subscriber unit 30 are similar to those in 3 parts shown and described.

As in 5 the RF front end is shown 210 with the down mixer 212 coupled and able to receive RF signals. The RF front end 210 comprises an external receiving antenna and a low noise amplifier (LNA) (LNA = "low noise amplifier"). In an alternative embodiment, and in particular for digital beam shaping, the RF front end comprises 210 an LNA, a mixer and an A / D converter in one integrated unit.

The received RF signal is sent to the down mixer 212 Posted. The down mixer 212 receives the RF signal and converts it to an IF signal using a signal from the TDMA or CDMA-LO signal, e.g. B. IF = RF-LO. The IF signal is then converted to a digital signal by the A / D converter 214 and the TDMA channelizers / demodulators 216 or the CDMA channelizers / demodulators 218 entered. The channelizers / demodulators 216 . 218 channel the digital IF signal into the desired narrow frequency channel and demodulate it to generate channel bits which are generated by the channelizers / demodulators 216 or 218 can be spent.

6 Figure 4 shows a flow diagram of a channel acquisition and management method in accordance with a preferred embodiment of the present invention. The procedure 300 comprises the acquisition process which finds either a CDMA pilot channel or a TDMA broadcast channel and determines whether a CDMA or a TDMA traffic channel is to be used for communication between the subscriber unit and a satellite or a base station. The procedure 300 also includes traffic channel management decision and traffic channel connection maintenance functions. Some of the steps in the process 300 are carried out by a satellite and / or a base station and some are carried out by a subscriber unit. For purposes of discussion, reference should be made to a satellite, although a base station can perform the same functions or steps as are performed by the satellite.

The procedure 300 starts at step 302 when a subscriber unit wants to access a traffic channel in order to make a telephone call with a destination. The subscriber unit searches for a CDMA pilot signal or a TDMA broadcast signal. In step 302 of 6 the subscriber unit determines whether a CDMA pilot signal or a TDMA broadcast signal is accessible. If neither a CDMA pilot signal nor a TDMA broadcast signal is accessible, the access fails in step 304 and the procedure 300 ends. Otherwise, since the subscriber unit is able to receive and demodulate either a CDMA pilot signal or a TDMA broadcast signal, it will look for the existence of one or both of these channels by using the LO signal to down-convert the appropriate IF frequency is modified and then this signal is routed to the CDMA or TDMA channelizer / demodulator. After demodulation (successful reception accepted), the subscriber unit can examine the data bits to determine the acquisition channel information in either the CDMA or TDMA system. With this information, the subscriber unit can now step 306 access either the CDMA or TDMA system of your choice based on signal strength, preference or availability.

Once the subscriber unit in step 306 either a CDMA pilot channel or a TDMA broadcast channel is acquired, a channel request is made to the satellite. The satellite then determines in step 308 according to the in 7 shown channel management process, which is described in detail below, whether there is an available traffic channel. After the satellite has found an available traffic channel, the channel assignment in step 310 sent to the subscriber unit and the subscriber unit begins communication over the traffic channel in step 312 , In step, the subscriber unit uses the traffic channel 314 the connection maintenance is carried out by the satellites, the base station and / or the subscriber unit. The connection maintenance allows modifications of the performance level as well as the user environment changes and optimization of frequency / code assignments according to changing load.

If in step 308 and after step 314 If no channel is available, the process ends 300 , It is important to understand that a subscriber unit can access a CDMA pilot channel, but the satellite / base station can determine that the subscriber unit should use a TDMA traffic channel instead. If so, the subscriber unit will switch to a TDMA traffic channel at the request of the satellite. The opposite is also true if the subscriber unit accesses a TDMA broadcast channel but is assigned a CDMA traffic channel by the satellite.

7 shows a flowchart of a channel management method 308 according to a preferred embodiment of the invention. Whenever a step can be performed by a satellite, it can also be performed by a base station, although only one satellite is referred to. The process begins in step 307 ( 6 ) when the subscriber unit sends a channel request to a satellite. The satellite determines in step 402 whether the subscriber unit making the request is able to operate using TDMA, CDMA, or both. The ability of the subscriber unit is communicated via the channel request in a number of different ways known to those skilled in the art. Some subscriber units can communicate using TDMA or CDMA. While other subscriber units can only communicate using one access scheme, but not both.

Once the satellite in step 402 determines the ability of the subscriber unit, the satellite calculates in step 404 the traffic load on the satellite in a reuse area. The impact of the interference generated by surrounding rays in the reuse area must be evaluated. There are a variety of ways to calculate satellite and traffic usage in the reuse area that are well known to those skilled in the art. After the satellite in step 404 calculates the traffic load of the satellite and the reuse area, the satellite selects a preferred access method (e.g. CDMA, TDMA or a combination) for the uplink and / or downlink based on the load analysis.

Table 1 represents below an example of the available Options based on the load on the neighboring cell and the current one Cell loading when both TDMA and CDMA schemes do the same Use spectrum.

Tabelle 1

Table 1

For example, if the load on the neighboring cell is low but the current cell is experiencing a high load, the satellite would select TDMA as the access scheme for the subscriber unit according to Table 1. If the loads on the neighboring cells and the current cell are low, the satellite would have a choice of using TDMA or CDMA. Table 1 represents only an example of what a satellite can choose based on the load conditions of the neighboring cells and the current cell. Other tables for selecting whether the subscriber unit communicates via TDMA or CDMA could be devised based on similar criteria as used in Table 1 or other factors well known to those skilled in the art.

The satellite can also choose that the uplink and the downlink have the same modulation scheme or that a different one Access technology for the uplink across from the downlink is used. Table 2 lists the four different access options for the uplink and the downlink on.

Tabelle 2

Table 2

Once the satellite in step 406 selects which access method is to be used for the uplink and the downlink, the satellite checks in step 408 to see if the communication hardware is available and in step 410 whether there is an available spectrum. If the satellite in step 412 determines that the channel (or channels) are available for the subscriber unit, the satellite transmits in step 310 ( 6 ) the channel assignment to the subscriber unit. Otherwise, the satellite determines in step 414 whether any other access options are available. If other access options are left, the satellite returns to step 406 , shown in 7 , back to choose the next best access method. The satellite repeats the steps 406 . 408 . 410 . 412 and 414 until a channel is found or until access is no longer possible. If it is in step 414 If there are no other access options, this indicates that the satellite was unable to find an available channel and the methods of 6 and 7 end until the next channel access cycle.

There are many advantages to the present Invention. An advantage of the invention is TDMA and CDMA in one Combine satellite communications system. Another advantage the invention is that the subscriber units are segmented in using one access scheme over another on peaks or load capacity needs. Another advantage of the invention is that the subscriber unit has a different access scheme on the uplink can use as the one on the downlink is used.

Accordingly, all of the appended claims are intended to Modifications of the invention are included in the scope of the invention as claimed.

Claims (4)

Method for use in a dual mode satellite communication network, comprising the steps: a) Finding either a CDMA pilot channel (CDMA = code division multiple access / multiple access in code multiplex) or a TDMA broadcasting channel (TDMA = time division multiple access / multiple access in time multiplex); and b) determining whether a CDMA traffic channel or a TDMA traffic channel between a subscriber unit and a satellite is to be used; wherein step (b) continues the steps include: Determine whether the subscriber unit in the TDMA, CDMA or both can work; Calculate a traffic load the satellite and a reuse area; and Choose whether CDMA or TDMA or a combination for an uplink and a downlink should be used based on the traffic load of the satellite and the reuse area. The method of claim 1, wherein step (a) further the steps include: a subscriber unit determines whether the CDMA pilot channel or to use the TDMA broadcast channel based on Signal strength, Preferential or availability. The method of claim 1, wherein step (b) further comprises the step of a satellite determining whether the CDMA traffic channel or the TDMA traffic channel between the subscriber unit and a base station tion should be used. The method of claim 1, wherein step (b) further the step includes that a base station determines whether the CDMA traffic channel or the TDMA traffic channel between the subscriber unit and a base station should be used.